DNA Barcoding In Chinese Fig Wasps

Figs (Moraceae, Ficus) and pollinating wasps (Hymenoptera, Agaoninae) are usually considered as the classic model of co-evolution due to their morphology, physiology and behavioural co-adaptation. According to whether pollinate figs, fig wasps can be divided into pollinating wasps and non-pollinating wasps. Pollinator wasps pollinate the figs, and figs provide the resources and habits for fig wasps'development, that is the well-known mutualism relationship. In most cases, each fig tree species is pollinated by one special pollinator wasp species, however, more and more studies has ruined the strict"one-to-one"rule which make the mutualism system more complex. Similarly, non-pollinators, major components of the figs-wasps system, attract much attention, especially for their host specificity.As we know, all kinds of researches on fig and fig wasps must be base on correct and valid taxonomy studies. However, the taxonomy of fig wasps faces the big problem such as extreme sexual dimorphism and male polymorphism which are not easily fixed just on morphological character. In addition, the fact that many species of non-pollinating wasps, from various subfamilies or families, exist in one fig species complicates the fig wasp system. All these extraordinary phenomena hinder scientists from correctly recognizing the different species and matching sexual individuals of cospecies, especially for non-pollinating wasps. Therefore, it is urgent to combine effective molecular method and morphology to fix the problem of fig wasps taxonomy system.Paul (2003) raised the point that we should choose one standard gene fragment as new"taxonomy character"to help traditional taxonomy. The mtDNA COI fragment is a core gene employed by DNA barcoding initiatives and has the potential to facilitate both the identification of known species and the discovery of new ones. Although there are some limitations like young species, close species, ancient polymorphism and Wolbachia infection, many studies have demonstrated that DNA barcodes are effective in diagnosing most species, such as insects, fishes, birds, plants etc.In this study, we DNA barcoded 2256 wasp samples belonging to 24 genera of 7 subfamilies and 6 families reared from 38 different fig species in 5 provinces of Southern China. We asked whether COI barcode could correctly distinguish species, match sexual individuals of cospecies with extreme dimorphism, identify host-specificity etc. We got 189 species out of 388 provisional morphology morphs by gene sequences, and 95% sexual female individuals match male individuals. Barcoding analysis revealed that the cryptic species of Chinese fig wasps mostly due to geographic area differences, pollinator wasps have more geographic cryptic species than non-pollinator wasps. Moreover, two geographic pollinators pollinate one fig species and two sympatric pollinators exist in one fig species respectively were found. Some species from non-pollinator genera, Walkerella, Philotrypesis, Sycoscapter, can attack several fig species, which indicating host-switch for these wasp species. In addition, it is necessary to combine common primer and specific primer to avoid contaminative species gene amplification in DNA bacoding program.Although the genus Sycophila has broad host preferences, some species are specifically associated with figs as non-pollinator wasps. Because of their sexual dimorphism, morphological plasticity, cryptic mating behaviour and poorly known biology, species identifications are often uncertain. It is particularly difficult to match con-specific females and males. Although some studies have suggested that Sycophila are not highly host-specific, the morphological characters differentiating females are very subtle, making it difficult to be certain that a single species uses multiple hosts. Nevertheless, its high species diversity and broad host use make Sycophila an excellent potential model system for the investigation of speciation patterns and host specificity. In this study, we employed two molecular markers, mitochondrial COI and nuclear ITS2, to identify Sycophila from six Chinese fig species. The primary goal of this study was to clarify the diversity of Sycophila species on single fig species and the extent of host specialization in the community found in association with six monoecious Ficus species in southern China. Morphological studies revealed 25 female and male morphs, while sequence results for both genes were consistent in supporting the presence of 15 species, of which 13 were host specialists and two used dual hosts. A single species of Sycophila was respectively found on four fig species, but six species were isolated from Ficus benjamina and a same number was reared from Ficus microcarpa. Sequence results revealed three male morphs in one species and detected two species that were overlooked by morphological analysis.